1. Field of the Invention
The present invention relates to a novel compound that exhibits enzyme inhibitory activity against prolyl endopeptidase (EC. 3.4.21.26). The invention also relates to a method for chemical synthesis of such novel compounds, as well as a prolyl endopeptidase activity inhibitor that contains said compound as the active ingredient.
Prolyl endopeptidase is known to inactivate neurotransmitters such as substance P, thyrotropin-releasing hormone (TRH) and neurotensin, or vasopressin speculatively associated with memory. Tsuru and Yoshimoto of the Department of Pharmaceutical Sciences, Nagasaki University, found that compounds capable of inhibiting prolyl endopeptidase activity were effective in preventing experimental amnesia caused in rats by scopolamine. Based on this discovery, they suggested the potential use of anti-prolyl endopeptidase substances as anti-amnesic agents.
Motivated by the report of Tsuru and Yoshimoto, the present inventors have made various efforts to find novel compounds that exhibit strong inhibitory activity against prolyl endopeptidase as an anti-amnesic activity and which yet display satisfactorily low toxicity levels.
2. Prior Art
U.S. patent applications Ser. No. 760,411 (filed on July 30, 1985), Ser. No. 852,709 (filed on Apr. 16, 1986), Ser. No. 852,710 (filed on Apr. 16, 1986) and Ser. No. 852,711 (filed on Apr. 16, 1986), now U.S. Pat. No. 4,701,465 patented Oct. 20, 1987, all of which have been assigned to the assignee of this invention, disclose certain types of compounds which have inhibitory activity against prolyl endopeptidase and are thus effective in treating amnesia.